3017

• UCREFRP Catalog Number: 3017
• Author: Suttkus, R. D. and G. H. Clemmer.
• Title: The Humpback Chub,
• USFW Year: 1977.
• Copyright Material: NO

4

counts presented in Table 1 show agreement with other
data by the various authors. Vertebral counts reported
by Holden and Stalnaker (1970) did not include the
Weberian complex (four vertebrae), thus when four is
added to the counts presented in their Table 2 the range
in the count becomes 46-49 which is inclusive in our
counts (45-49) presented in Table 1.
In addition to the above counts we counted the prin-
cipal caudal rays and contrary to the count of 20 given
by Miller (1946) for the holotype, we found that 95 of
the 96 specimens had 19 caudal rays. The one atypical
count was 18.
The lateral line scale count was difficult to make on
some specimens, but even on those specimens the accu-
racy is within plus or minus two scales. Many specimens
had undulations in the lateral line row of scales, particu-
larly in the anterior portion. On a few specimens the
lateral line row had displaced sections of one to several
scales.
Pharyngeal arches were removed from twenty speci-
mens to determine nature of dentition. Miller (1946)
gave the dental formula of the holotype as 2,5 - 4,l? He
said there may have been a second tooth in the minor
row on the right arch. Seventeen of the twenty specimens
we examined have the typical Gila dental formula of
2,5 - 4,2. One specimen has 2,5 - 4,1, another specimen
has 1,5 - 4,2, and the remaining specimen of the twenty
examined has 2,5 - 5,2. The extra tooth on the right
arch is somewhat medial and practically has a common
base with the upper tooth of the major row. There is a
possibility that the two specimens with the single tooth
in the minor row on the one side did have two teeth and
one was broken off without leaving a trace of a stump
or a socket. However, the count may be correct in that
some specimens have very slender, delicate teeth in the
minor row and it is conceivable that this may be an in-
dication of a reduction in number.
X-rays of the larger specimens revealed a two-cham-
bered swim bladder.
A review of the 24 scattergrams (Figures 1 - 8) of pro-
portional measurements indicates a linear relationship
of all proportions with the standard length. Some obser-
vations do not appear on the scattergrams because of
overlap, but all data for each proportion were used to
compute regression formulae.

Sexual Dimorphism

Some males have decidedly longer pectoral and pelvic
fins than most females; however, a few females have
rather long paired fins. The relative position, size and
shape of the tubular termination of the digestive tract
(outlined with ink on illustrations) and the urogenital
papilla are quite different in the female and the male.
Figure 18 illustrates the anal region of an adult female,
and Figure 19 illustrates that of an adult male. The
tubular ending of the digestive tract of the female is long
and extended posteriorly (overlapping base of first anal
fin ray) so that the urogenital papilla is hidden under-

TULANE UNIVERSITY MUSEUM NATURAL HISTORY

neath when viewing the ventral surface of the fish. In
the male the terminal tube of the digestive tract is not
nearly so long and the urogenital papilla (indicated by
arrow on illustration) projects ventrally so that its tip is
visible just beyond the termination of the digestive tract.
Tuberculation of males and females differ consider-
ably. The nuptial male has larger tubercles and more
areas of the fins and body are studded with tubercles
than on the nuptial female. One of the four adult speci-
mens (TU 97918) collected from the mouth of Little
Colorado River during June of 1976 has small breeding
tubercles scattered over the top of the head, laterally to
the rim of the orbit and about half way ventrally on the
opercle. There is a progressively decreasing number of
tubercles on the hump from the nape toward the origin
of the dorsal fin. Tubercles extend nearly two-thirds the
distance toward the dorsal fin. There are no tubercles
on the underside of head, about the lips nor below the
orbit on the snout or cheek. Although the anteromedial
patches of scales in front of the bases of the pectoral fins
(breast patches) are developed with free posterior mar-
gins, there are none with developed tubercular ridges.
There are small tubercles developed on the upper surface
of the second, third and fourth pectoral fin rays and also
on the upper surface of the second, third, fourth and
fifth pelvic rays. We consider the above male fish to rep-
resent an early stage of nuptial development.
The salvage specimens (TU 100542) obtained from
Powell Reservoir were near spawning condition if not
actually spawning at the time of capture. The larger
specimen (Figure 17 lower) is a female (320 mm SL)
and the smaller (Figure 17 upper) a male (298 mm SL) .
Unfortunately we did not obtain the specimens until a
number of months after they had been captured on 5
June 1975. The specimens exhibited some breeding color
even after having been frozen and stored in a freezer.
The entire lower side below dark pigmentation of the
body of the male was orange. The bases of pectoral and
anal fins were orange. The cheek below the eye was
yellowish and the iris was pinkish-orange. The female
was light orange on the lower portion of the side and at
the base of the anal fin. The base of the pectoral fin
was cream color. These colors may have been brighter
at the time of capture.
The tubercles and thickened epidermal layer had
sloughed off various parts of the body of these two speci-
mens during the delay in getting the specimens from the
field to the freezer and then subsequent freezing and
thawing. However, sufficient tuberculation remains to
allow a description of the sexual dimorphism in this
character. The male has rather large tubercles scattered
over the entire head (Figures 20 and 21) and smaller
ones p~steriorly on the hump to about two-thirds the
distance toward the origin of the dorsal fin. The thick-
ened epidermal layer is missing from part of this region,
and perhaps, tubercles were present all the way to the
dorsal fin. These predorsal tubercles are not particularly
associated with the embedded scales but are scattered
over the surface. Some tubercles occur over the scales